# Pavement Design Questions and Answers – Rigid Pavement Design

This set of Pavement Design Multiple Choice Questions & Answers (MCQs) focuses on “Rigid Pavement Design”.

1. Which of the below is not a type of force acting on the cement concrete pavement?
a) Environmental changes
b) Drying shrinkage

Explanation: There are mainly three categories of loads acting on the rigid pavement. They are the environmental changes, drying shrinkage and the traffic loads. Ductile loads are not considered in case of rigid pavements but are taken care of in flexible pavements.

2. Which IRC code is used for the design of rigid pavements in rural areas?
a) IRC 58:2002
b) IRC SP 58:2004
c) IRC SP 62:2004
d) IRC 62:2002

Explanation: The code for guidelines to design the rigid pavement in rural areas is IRC SP 62:2004. IRC 58:2002 is the code used for the design of rigid pavements for highways. IRC has provided separate guidelines for pavement design in various locations.

3. The traffic load data is not helpful in determining which of the below parameters?
a) Pavement composition
b) Pavement thickness
c) Pavement layer type
d) Number of pavement layers

Explanation: Traffic data is collected prior to the designing process, so as to analyze the data and determine the necessary parameters. The parameters are pavement composition, layer type and thickness. The data about the subgrade decides the number of layers required.

4. Who was the first person to help analyze the rigid pavement design methods?
a) H. M. Westerngaard
b) H. M. Westergaard
c) H. M. Westergaurd
d) H. M. Westegaard

Explanation: H. M. Westergaard was the person who pioneered the rational treatment of the problem of the analysis of the rigid pavements. He developed equations and models to help identify and simplify the design process.

5. What is the main design criterion for designing the rigid pavement?
a) Tensile stress
b) Compressive stress
c) Fatigue stress
d) Shear stress

Explanation: Rigid pavement is not flexible i.e. it is not elastic in nature. The deformations once formed due to the tensile stress are not reversible. They tend to develop into big cracks later on. Tensile stress is the main factor to be considered in the design process.

6. What is the design life for a cement concrete pavement?
a) 20 years
b) 25 years
c) 30 years
d) 35 years

Explanation: Design life of a pavement is predicted after a considerable amount of data collection and the analysis of the same. Normally 30 years is the design life of the cement concrete pavement. It can be taken as 20 if sufficient traffic data is not available or for low volume roads.

7. The strength of the sub-base decides the strength of the rigid pavement.
a) True
b) False

Explanation: In rigid pavements, the strength is taken up by the concrete slab that is placed on top of the base or sub-base course. Slab action helps in transferring the loads to the lower layers. The sub-base course doesn’t define the strength of the pavement.

8. Westergaard’s modulus of subgrade reaction is denoted by which symbol?
a) k
b) w
c) Wk
d) Kw

Explanation: Westergaard’s modulus of subgrade reaction is denoted by the symbol k. It is similar to the subgrade support and is obtained from the plate load test as the ratio of pressure to deflection. The deflection to calculate the value of k is taken as 0.125 cm.

9. What does LSF stand for?
b) Low Stress Force
d) Low Stress Factor

Explanation: The term LSF stands for Load Safety Factor. When the stress in the pavement is calculated, the magnitude of axle load is multiplied using the load safety factor. The LSF takes care of the unpredicted heavy truck loads.

10. The traffic data for the analysis is obtained by referring to which code?
a) IRC 9
b) IRC 8
c) IRC 10
d) IRC 11

Explanation: IRC 9 has the details of the traffic census on non-urban roads. So, for the design traffic computation, first the assessment of average traffic based on seven days 24-hour data is made. Then the data from IRC 9 is referred to and the final conclusions are made.

11. What is the formula to find the value of k if a plate of diameter 30 cm is used instead of the standard 75 cm?
a) k75=0.5/k30
b) k75=0.5×k30
c) k30=0.5×k75
d) k30=0.5/k75

Explanation: As per the details given in IRC 58:2002, the standard diameter used in the plate load test for finding the value of k is 75 cm. in some cases, smaller diameter plates can be used. But these have to be converted to standard values, k75=0.5×k30 gives the relation for the same.

12. What is the tyre pressure generally taken for the design purpose?
a) 1 MPa
b) 0.9 MPa
c) 0.8 MPa
d) 0.7 MPa

Explanation: The tyre pressure of the commercial vehicles on the highway ranges from 0.7 to 1 MPa. This does not affect the stresses in concrete pavement having thickness as or above 20 cm. so, generally for the design purpose a tyre pressure of 0.8 MPa is taken.

13. The design of the slab is done for 85th percentile axle load.
a) True
b) False

Explanation: The basic design of the cement concrete slab is done with 98th percentile axle load and not 85th percentile load. The design after that can be checked for fatigue consumption for higher axle loads. IRC 58:2002 outlines this criterion.

14. What is the LSF for roads having a low volume of truck traffic taken as?
a) 1
b) 1.1
c) 1.2
d) 1.3

Explanation: The LSF values for various conditions have been given in IRC 58:2002. According to which, LSF for roads having high truck traffic is 1.2, for roads with low truck traffic is 1.1 and for residential and other streets, it is 1.

15. If the traffic growth rate is not available, ______ is assumed to be the growth rate.
a) 7.5%
b) 5%
c) 5.5%
d) 7%

Explanation: Sometimes, it is not possible to obtain the growth rate of the traffic if the actual data is not available. In such cases, as per the recommendations by IRC 58:2002, the growth rate can be assumed to be 7.5%.

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